The present invention relates generally to roller apparatus such as, for example, back-up rollers used to support work rolls.
Work rolls are used in tandem sets to shape metal through compressive forces. The supporting back-up rollers tend to have a relatively larger diameter than the work rolls. Back-up rollers must be capable of applying very high forces, as much as 300,000 pounds of force.
Conventional back-up rollers comprise a bearing in which the axle is received in the inner race and the outer race is received in the roller. Bearing elements such as ball or cylindrical members are rotatably received between the races so that the roller is rotatable relative to the axle. Since there are size constraints on the rollers, the wall thickness of each of the inner and outer races for back-up roller bearings is conventionally limited to typically no more than about xc2xd inch. Bearings, for example, for cam followers and bearing wheels, have been provided wherein the wall thicknesses of the inner and outer races have been in excess of 1 inch. The rigidity of a race is related to its effective wall thickness (which includes the thickness of an axle or roller to which it is rigidly mounted), and the bearing capacity is a function of the rigidity of the races. Thus, the capacity of such conventional back-up rollers is limited by the rigidity of the least rigid of the races.
Back-up bearings have been provided wherein the inner race is mounted over an axle and has a variable thickness ranging between about xc2xe inch and about 1{fraction (1/16)} inch and wherein the outer race serves as the roller and has a variable thickness in excess of about 3 inches and the surface of which has a shore hardness of 78 to 83.
One type of back-up roller heretofore provided by Applicant to a customer comprises two spherical roller bearings with an inner race fitted to an axle and an outer race fitted to an outer shell or roller composed of AISI 4140 heat-treated steel having a Rockwell C hardness of 45. Both the bearing life and the shell life were however considered unacceptable. In order to improve the shell life and also hopefully the bearing life, the customer requested that the shell be made instead of cast 420 stainless steel having a Rockwell C hardness of 50. While this did improve the shell life, the bearing life nevertheless remained unacceptable to the customer.
As the back-up rollers wear and their outer diameters accordingly decrease, they do not bear as hard against the work rolls with the result that the work rolls are undesirably more prone to deflect. When this occurs, it has been necessary with conventional back-up rollers to replace a worn roller with a new one. It is, however, considered desirable to increase the useful life of the back-up rollers so that they may need replacement less often.
It is accordingly an object of the present invention to extend the useful life of the back-up rollers.
It is a further object of the present invention to simplify construction of such extended life back-up rollers while providing suitable back-up roller capacity.
In order to simplify construction of a back-up roller and provide suitable capacity thereof, in accordance with the present invention, an axle and roller serve as the inner and outer bearing races respectively, and each preferably has a thickness radially of at least about 1 inch to achieve suitable capacity.
In order to extend the useful life of such a back-up roller, in accordance with the present invention, the height (distance from the back-up roller axle to the back-up roller circumference or radially outer surface) thereof is adjustable by rotating an eccentric mount through which the axle is disposed and thereby translating the roller in a radial direction thereof. Preferably, in order to rotate the eccentric bushing, circumferential slot means is provided in the eccentric bushing, and force is applied to the eccentric bushing at ends respectively of the slot means to push the eccentric bushing in opposite circumferential directions respectively.
Back-up rollers are placed at spaced positions both circumferentially about (from overhead and from the floor) and axially along the work rolls. Each back-up roller must be accurately positioned, both top to bottom and left to right, and custom precision grinding is required to achieve the necessary accuracy during every changeover.
A set of experimental back-up rollers with eccentric mounts were installed for the customer in 1995. Since the installation was experimental, it was necessary to provide the customer with essentially unconditional support, which has continued to the present, to get the back-up rollers to work, and, since 1995, various modifications have been tried to address various problems. The major modifications are discussed hereinafter. Only during the current year, 2000, has it become apparent from various test and performance data including roller life data that the back-up roller has been improved to such an extent that it may now be sold to other customers. Applicant has not sold or offered for sale or even shown to other customers the back-up roller due to its experimental nature. While a longer roller life was based in 1995 on calculations and thus theoretical, performance data in 1998 indicated that the rollers were wearing too fast and thus unacceptably not giving the desired roller life. Modifications to reduce roller wear and thus provide the desired longer life were then made. It was not until this year, 2000, that it was confirmed with test and performance data from the modifications made in 1998 that, with additional improvements made in 2000, the desired roller life would finally be achieved. There have also been problems over the years since the installation other than the roller wear problem to be solved before the roller apparatus could be considered viable as a commercial product. It was, for example, necessary to improve the eccentric bushing placement so that it stayed tight and did not damage the housing and then to confirm that it would remain tight over a long period of time (years). Another major problem was insufficiency of the amount of height adjustment.
It is also important that, after any height adjustment, all of the roller elements share the load.
As initially installed, the roller height was adjustable through about 0.008 inch. It was discovered that the end plates (which enclose the rolling elements at the ends and which are fitted in cutouts in the roller) were cracking. This was corrected by increasing the radiuses of end plate corners and corresponding cutout corners from about {fraction (1/32)} inch to about {fraction (3/32)} inch and by press fitting (instead of slip-fitting) the end plates into position in order to reduce distortion and flexing of the roller. A bevel was also added to the roller to reduce stresses in the roller corners.
In order to improve the bearing life, the back-up rollers were made with the inner race serving as the axle and the outer race serving as the roller, and the outer race was made of a two-piece or laminated construction comprising an outer member of cast 420 stainless steel having a Rockwell C hardness of 50 (so as to not mark the work rolls) and a harder inner sleeve of AISI 52100 bearing steel having a Rockwell C hardness of 60. When test results showed in 1998 that, although the back-up roller assembly life had been improved, the outer members were wearing and in some cases fatiguing (cracks in corners of end plates) too rapidly, they were improved by making the roller as a single piece of D2 tool steel having a Rockwell C hardness of 60 (option 1) for higher wear resistance as well as strength and hardness. Additional test results in 2000 indicated that the back-up rollers were performing as desired, but, because of the increased hardness of the D2 tool steel material, the life of the work rolls was reduced. It is now believed that by constructing the roller inner sleeve of AISI 52100 bearing steel having a Rockwell C hardness of 62 and the roller outer member of forged 420 stainless steel having a Rockwell C hardness of 52 (option 2), ideal wear of both the outer and inner members of the roller as well as the work roll should now be achieved. It was also discovered that some applications are of such a severe nature that the benefit of the robust construction of the solid D2 roller (option 1) would outweigh the reduced life (increased wear) of the work roll, and, accordingly, it has been decided to offer both options 1 and 2 to customers.
It was also discovered that the rolling or bearing element spacers were too tight against the axle and not adequately sharing the load and that the grease was not flowing well from the middle to the outside rolling elements. This was remedied along with the wear improvements made in 1998 by scalloping (making semi-circular cutouts) the circular edges defining the inner diameters of the spacers and by increasing the spacer outer diameter to give back surface area lost due to the scalloping. The flatness of the spacers was increased to reduce the amount of acceptable wavyness (for tighter tolerance).
It was further found that the eccentric bushing was not staying tight enough within its housing, and this was remedied by making the housing cap out of armor plate (1xc2xd inch thick) instead of standard carbon steel.
It was also found that the amount of eccentric adjustment was insufficient especially in view of the need to adjust for inaccuracies in set-up. The angle of a pair of slots used for adjustment of the eccentric bushing was increased from 46 to 73 degrees to obtain the necessary amount of roller adjustment. When it was found that this did not achieve the desired amount of roller adjustment since adjusting set screws were oriented generally at tangents to the slots respectively, the angle was reduced to about 50.54 degrees, as illustrated at 21 in FIG. 1.
The roller apparatus of the present invention as modified by the 1998 improvements is shown in FIGS. 1 to 3 of the drawings.
The roller performance after the 1998 improvements, especially a finding that the problem of insufficient eccentric adjustment had still not been solved, indicated the need for still further improvements, which were made in the year 2000. The roller apparatus of the present invention as modified by the year 2000 improvements is shown in FIGS. 4 to 6 of the drawings.
One of the year 2000 improvements is the provision of an increased length to a closed-off grease slot to 1xe2x85x9c inch so as to open it up.
The achievable amount of roller translation or height adjustment of the eccentric bushing, which is desirably about plus or minus 0.018 inch or more (at least about 0.015 inch), was still unduly limited, i.e., only about plus or minus 0.012 inch. Thus, there was some cause other than slot length for the limited height adjustment. This problem was corrected by the improvements made in the year 2000 and discussed with reference to FIGS. 4 to 6 of the drawings.
It is accordingly an object of an aspect of the present invention to achieve adequate height adjustment for the back-up roller.
In order to achieve adequate height adjustment for the back-up roller, in accordance with an aspect of the present invention, as shown in FIGS. 4 and 5 of the drawings, a portion of the eccentric bushing between the slots, which was found to be interfering with the movement of the adjustment set screws into the slots, was removed by extending the slots to each other thus making the pair of slots into one single slot.
The above and other objects, features, and advantages of the present invention will be apparent in the following detailed description of the preferred embodiments thereof when read in conjunction with the accompanying drawings wherein the same reference numerals denote the same or similar parts throughout the several views.